This application claims the benefit of Japanese Patent Application No. 2004-188696 filed in Japan on Jun. 25, 2004, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an in-vehicle antenna apparatus mounted on a windowpane of a vehicle, such as an automobile, and particularly, to an electronic circuit unit attached to a surface of a sheet of glass facing the inside of a vehicle, the sheet of glass being, for example, rear glass or front glass installed in a vehicle at an angle with respect to the ground.
2. Description of the Related Art
A conventional in-vehicle antenna apparatus is provided with a radiation conductor disposed on an inner surface of rear glass or front glass of a vehicle, and an electronic circuit unit that includes a pre-amplifying circuit and that is attached to the inner surface, such that the in-vehicle antenna apparatus is capable of, for example, receiving a circularly-polarized wave or a linearly-polarized wave sent from a satellite or a ground-based station. In comparison with other types of antenna apparatuses that are set on the exterior of a vehicle, such as a roof, this type of antenna apparatus is advantageous in having a longer lifespan and a lower possibility of being stolen. Furthermore, in comparison with antenna apparatuses that are set in the vicinity of the inner surface of a windowpane of a vehicle, this type of antenna apparatus is advantageous in providing a good space factor and a wide angle of view.
In an in-vehicle antenna apparatus of this type, the electronic circuit unit attached to the inner surface of a sheet of glass, such as rear glass or front glass, facing the inside of the vehicle includes a housing that houses a circuit substrate provided with, for example, a pre-amplifying circuit. In the electronic circuit unit, a radiation conductor having a predetermined shape and disposed on the sheet of glass is electrically connected with the circuit substrate via appropriate means so that the radiation conductor can receive electricity and load a received signal.
Japanese Unexamined Patent Application Publication No. 6-53722 (p. 2 to p. 3, FIG. 1) discloses an example of such a conventional in-vehicle antenna apparatus in which a conductor segment protrudes from an insulating housing that houses a circuit substrate such that the conductor segment is soldered on an electric feeding point of a radiation conductor. Since one end of the conductor segment is connected to an input section of a pre-amplifying circuit inside the housing, the radiation conductor and the pre-amplifying circuit are electrically connected to each other via the conductor segment, and the electronic circuit unit is fixed on the sheet of glass.
In this type of in-vehicle antenna apparatus mounted on the inner surface of the rear glass or the front glass of the vehicle, the electronic circuit unit is advantageously protected from rainwater and water from car wash. However, due to the fact that the vehicle interior tends to become in a high humidity state quite easily, dewdrops often form on the inner surface of the sheet of glass. For this reason, water droplets can easily enter the internal space of the electronic circuit unit. Moreover, since there are often cases where the sheet of glass is cleaned from the vehicle interior side using water and detergent, it is highly possible that water droplets may enter the internal space of the electronic circuit unit during the cleaning process. For this reason, unless an appropriate drainage treatment is performed, the water may accumulate in the internal space of the electronic circuit unit. This may lead to a malfunction or failure if, for example, a component-holding surface of the circuit substrate is kept immersed in the water. Accordingly, due to the fact that specific drainage means is not provided, such a conventional in-vehicle antenna apparatus is problematic in that it could easily lead to lower reliability and shorter lifespan.